A typical escalator includes a frame, balustrades with movable handrails, steps, a drive system and a step chain for propelling the steps. The frame includes a truss section on both left and right hand sides of the frame. Each truss section has two end sections forming landings, which are connected by an inclined midsection. The upper landing usually houses the escalator drive system or machine positioned between the trusses.
The drive system of the escalator typically consists of a step chain, a step chain drive sprocket, an axle and a drive motor. The drive motor drives the step chain to travel a continuous closed loop.
As shown in FIGS. 1 and 2, steps 10, which are attached to a step chain 12, run from one landing to the other in order to transport the passengers.
Support levers 16 are fixedly coupled to both sides of the step 10. Each support lever 16 is provided with a step roller 18, which is rotatably mounted to an end of the support lever 16. The step roller 18 guides the movement of the step 10 and further supports the same.
An escalator has a track 20 on both left and right sides, along which the step roller 18 travels a continuous closed loop. The track 20 is substantially parabolic in shape at the turn around areas, which are located under the lower and upper landings, so that the step roller 18 and the step 10 can make a 180 degree heading change at the turn around areas.
The track 20 includes an inner rail 24 and an outer rail 22 that is disposed outward of the inner rail 24. The gap between the inner rail 24 and the outer rail 22 is set to be a little larger than the diameter of the step roller 18. The outer rail 22 has a L-shape to prevent the step roller 18 from separating transversely from the track 20.
At the passenger conveying area, the step roller 18 rolls on the inner rail 24 of the track 20. Since the step 10 moves upward, the step roller 18 rises from the inner rail 24 to the outer rail 22 when the step roller 18 advances into the curved portion of the track 20 at the upper turn around area. This is due to the inertia of the moving step 10. As such, the step roller 18 collides with the outer rail 22. Then, the step roller 18 descends toward the lower landing with rolling on the outer rail 22 and returns onto the inner rail 24 at the lower turn around area.
However, the collisions of the step roller with the rails of the track cause undesired noise and vibration, thus making the passengers feel very uncomfortable. Such collisions may even lead to malfunction of the escalator.